1. Field of the Invention
The present invention relates to a clamp apparatus capable of clamping a workpiece by the aid of an arm which is rotatable by a predetermined angle in accordance with a driving action of a driving mechanism.
2. Description of the Related Art
A clamp cylinder has been hitherto used, for example, in order to clamp a constitutive part when the constitutive part of an automobile or the like is welded. Such a clamp cylinder is disclosed, for example, in U.S. Pat. No. 4,458,889.
The clamp cylinder disclosed in U.S. Pat. No. 4,458,889 is constructed as shown in FIGS. 9 and 10. That is, a piston rod 2, which is movable back and forth in accordance with the driving action of a cylinder 1c, is arranged between a pair divided bodies 1a, 1b. A coupling 3 is connected to a first end of the piston rod 2. A pair of links 5a, 5b and a pair of rollers 6a, 6b are rotatably attached to both side portions of the coupling 3 by the aid of a first shaft 4. An arm 8 is connected rotatably by a predetermined angle between the pair of links 5a, 5b by the aid of a second shaft 7.
In this arrangement, the pair of rollers 6a, 6b are provided slidably by the aid of a plurality of needles 9a which are installed to holes. The piston rod 2 is provided so that it is displaceable integrally with the rollers 6a, 6b in accordance with the guiding action of the rollers 6a, 6b which are slidable along track grooves 9b formed on the bodies 1a, 1b respectively.
However, the clamp cylinder disclosed in U.S. Pat. No. 4,458,889 concerning the conventional technique described above is not provided with a mechanism for holding the clamped state of a workpiece, for example, if the pressure fluid to be supplied to the cylinder 1c is stopped by any cause when the unillustrated workpiece is clamped by the arm 8. Therefore, it is feared that the clamped state of the workpiece may be canceled, and the workpiece may be disengaged.
A general object of the present invention is to provide a clamp apparatus which is capable of reliably maintaining the clamped state of a workpiece even when the supply of driving force to an arm is stopped.
A principal object of the present invention is to provide a clamp apparatus which makes it possible to avoid any excessive consumption of a pressure fluid so that the flow rate of the pressure fluid to be used may be reduced by commonly using the pressure fluid to be supplied into a pressure chamber and the pressure fluid to be supplied to a cylinder chamber.
Another object of the present invention is to provide a clamp apparatus which makes it possible to reliably cancel the locked state before a piston is displaced.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.